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Würth Engine Sealing Compound, Silicone Special 250

Würth Engine Sealing Compound, Silicone Special 250

0890321

23 in stock

Key Features

  • Permanently elastic, acetate-curing silicone sealant for engine, transmission, and bodywork applications subject to extreme temperatures and vibration.
  • Withstands continuous temperatures up to 250°C and brief thermal peaks up to 300°C without loss of sealing integrity.
  • Cold-vulcanising silicone rubber - cures at room temperature to form a flexible, resilient seal.
  • Bridges large surface irregularities and maintains a reliable seal even after long-term exposure to vibration and mechanical stress.
  • Excellent adhesion and chemical resistance, suitable for contact with oils, coolants, and automotive fluids.
  • Does not run, sag, or pull threads, allowing clean application and precise bead control.
  • Fast skin formation within 6-12 minutes; full vulcanisation rate approximately 1.5mm per day.
  • High flexibility with up to 25% continuous movement absorption below 150°C.
  • Temperature resistant from -50°C to 250°C, short-term up to 300°C.
  • Ideal for high-heat engine components and metal joints requiring flexibility and chemical durability.
£13.99 GBP
£13.99 GBP
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Product Product subtotal Quantity Price Product subtotal
Würth Engine Sealing Compound, Silicone Special 250
Würth Engine Sealing Compound, Silicone Special 2500890321
Würth Engine Sealing Compound, Silicone Special 2500890321
£13.99/ea 		£0.00
£13.99/ea £0.00

Description

High-Temperature, Permanently Elastic Silicone Sealant

Würth Engine Sealing Compound Silicone Special 250 is a professional-grade, acetate-curing silicone sealant designed for use in automotive, industrial, and bodywork applications where components are exposed to high temperatures, vibration, and chemical stress. It forms a cold-vulcanised, permanently elastic silicone rubber seal that provides reliable performance across a wide range of materials and environments.

Outstanding Temperature and Chemical Resistance

This sealant is formulated to withstand continuous exposure to heat up to 250°C , with short-term peaks up to 300°C, making it ideal for sealing engine and transmission housings, crankcases, oil pans, and cylinder head covers. It resists degradation from engine oils, coolants, lubricants, and fuels, ensuring long-lasting sealing under harsh operating conditions.

Cold-Vulcanising, Non-Sagging Formula

The product cures at room temperature into a flexible, elastic silicone rubber that bridges surface imperfections and unevenness. Its non-sagging consistency prevents the material from running or forming threads during application, ensuring precise, clean bead lines even on vertical or overhead surfaces.

Flexible and Vibration-Resistant

Once cured, Würth Silicone Special 250 maintains permanent elasticity with 25% movement absoption (below 150°C) and 18% at higher temperatures. This elasticity allows it to absorb vibrations and thermal expansion differences between materials, preventing cracking or separation over time.

Fast Skin Formation and Efficient Curing

The silicone begins to form a skin within 6-12 minutes, depending on humidity and temperature, and cures at approximately 1.5 mm per day. This allows quick assembly and minimal downtime in production or repair environments.

Versatile Application Range

Suitable for use in a wide variety of sealing and bonding applications across engines, mechanical systems, and bodywork, including:

  • Cylinder heads, crankcases, oil pans, and gear housings.
  • Radiators, differentials, and transmission covers.
  • Lighting housings, indicator assemblies, weld seams, and joints.

More Information

Application Instructions

  1. Ensure all surfaces are clean, dry, and free from oil, grease, and dust.
  2. Cut the cartridge nozzle to the desired bead width.
  3. Apply a continuous bead of sealant to one surface using a suitable applicator or cartridge gun.
  4. Assemble the components before skin formation (within approximately 6-12 minutes).
  5. Allow to cure at room temperature; curing rate is approx. 1.5 mm/day at 23°C and 50% relative humidity.
  6. Avoid excessive joint movement until the sealant is fully vulcanised.

Usage Notes

  • Processing temperature: 5°C to 40°C.
  • Temperature resistance: -50°C to 250°C (short term up to 300°C).
  • Store in a cool, dry area below 25°C.
  • Shelf life 18 months from production.
  • Ensure adequate air circulation during curing.

Specifications

Chemical Basis: Acetate-curing silicone

Colour: Red

Contents: 70 ml (73 g weight)

Density: 1.05 g/cm³ (at 20 °C)

Odour: Vinegar-like (acetic acid)

Skin Formation Time: 6–12 min (at 23 °C, 50% RH)

Curing Rate: Approx. 1.5 mm/day (at 23 °C, 50% RH)

Shore A Hardness: 30

Elongation at Break: 300 %

Continuous Movement Absorption:

• Up to 150 °C: 25 %

• Above 150 °C: 18 %

Temperature Resistance: -50 °C to +250 °C (short-term +300 °C)

Processing Temperature: +5 °C to +40 °C

Adhesion: Excellent on metals, glass, ceramics, and coated surfaces

Curing Mechanism: Acetoxy (acidic) curing system

Shelf Life: 18 months (cool, dry storage below 25 °C)

Corrosion Protection: Yes (non-corrosive to metals when cured)

Elasticity: Permanently elastic

Paint Compatibility: Not overpaintable

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